Multifunctional triazolylferrocenyl Janus dendron: Nanoparticle stabilizer, smart drug carrier and supramolecular nanoreactor

Article abstract of DOI:10.1002/aoc.4000

Owing to their unique broken symmetry, amphiphilic Janus dendrimers and dendons provide fascinating properties for material, biological, pharmaceutical and biomedical applications. The integration of various organometallic moieties into these macromolecul

Full text of DOI:10.1002/aoc.4000

Received: 6 April 2017
DOI: 10.1002/aoc.4000
Revised: 28 June 2017
Accepted: 29 June 2017
F U L L P A P E R
Multifunctional triazolylferrocenyl Janus dendron:
Nanoparticle stabilizer, smart drug carrier and
supramolecular nanoreactor
Li Zhao1,2 | Qiangjun Ling1 | Xiong Liu1,2 | Chaodong Hang1 | Qiuxia Zhao1,2
Fangfei Liu1,2 | Haibin Gu1,2
|
1 Key Laboratory of Leather Chemistry and
Owing to their unique broken symmetry, amphiphilic Janus dendrimers and
dendons provide fascinating properties for material, biological, pharmaceutical
and biomedical applications. The integration of various organometallic
moieties into these macromolecules will further offer the opportunity to form
complex and intelligent architectures and materials. Here, we report a novel,
simple and multifunctional Janus dendron containing redox‐reversible
hydrophobic ferrocene (Fc) unit, complexing‐effective 1,2,3‐triazole ligand
and biocompatible hydrophilic triethylene glycol termini. Silver and gold nano-
particles were firstly successfully prepared by using the Janus dendron as the
reducing agent of Au(III) and Ag(I), and the stabilizer of the corresponding
nanoparticles. The redox response of the Fc moiety was then employed to trig-
ger the release of model drug, rhodamine B, encapsulated in supramolecular
micelles formed by the self‐assembly of the Janus dendron. Finally, the precise
and excellent metal‐complexing ability of the triazole group in this dendron
was fully utilized to stabilize a water‐soluble Cu(I) catalyst, forming supramo-
lecular nanoreactors for the catalysis of the copper(I)‐catalyzed azide alkyne
cycloaddition click reaction in only water. The multifunctional characteristics
of this dendron highlight the potential for organometallic Janus dendrimers
and dendrons in the fields of functional materials and nanomedicines.
Engineering of Ministry of Education,
Sichuan University, Chengdu 610065,
China
2 National Engineering Laboratory for
Clean Technology of Leather
Manufacture, Sichuan University,
Chengdu 610065, China
Correspondence
Haibin Gu, Key Laboratory of Leather
Chemistry and Engineering of Ministry of
Education, Sichuan University, Chengdu
610065, China.
Email: guhaibinkong@126.com
KEYWORDS
CuAAC click chemistry, ferrocene chemistry, Janus dendrimers and dendrons, nanoreactors,
redox‐responsive, silver and gold nanoparticles
1 | INTRODUCTION
symmetry, and find various applications in the fields of
catalysis,[2] materials[3] and biology.[4,5]
Dendrimers are highly branched, well‐defined and mono-
disperse cauliflower‐shaped globular macromolecules
with high density of terminal groups, and are composed
of a central core, branching points, termini (at the periph-
ery) and inner cavities.[1] Conventional dendrimers
possess a single type of terminal group and exhibit high
Janus dendrimers (JDs) are newly emerging types of
dendrimers and are normally constructed of two different
dendrons with varying size and functionality to obtain a
single amphiphilic or heterofunctional macromole-
cule.[6–9] Their asymmetric structures lead to new and
efficient characteristic properties for the formation of
Appl Organometal Chem. 2017;e4000.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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ZHAO ET AL.
complex self‐assembled materials that are presently incon-
ceivable for homogeneous or symmetric dendrimers,[10]
and many applications have been investigated, especially
in the fields of materials and biology, such as thermal
actuators,[11] ionic liquids,[12] catalysis,[13] light harvesting
systems,[14] bioimaging,[15] optoelectronics[16] and drug
delivery.[17]
behave as electron reservoirs to provide electrostatic stabi-
lization.[33] This unique property is favorable for them to
be used as rare neutral single‐electron transfer reagents
for the reduction of Au(III) and Ag(I) in the synthesis of
gold nanoparticles (AuNPs)[33–41] and silver nanoparticles
(AgNPs),[39–44] and contribute to the stabilization of NPs
under ferricinium form. In the present work, JD 7 was
firstly applied as the reducing agent of Au(III) and
Ag(I), and the stabilizer of the corresponding NPs
(Figure 1). The redox response of the Fc moiety was then
employed to trigger the release of a model drug, rhoda-
mine B (RhB), encapsulated in supramolecular micelles
formed by the self‐assembly of JD 7. Finally, the precise
and excellent complexing ability to metal ions of the tri-
azole group[45] in 7 was fully utilized to stabilize a
water‐soluble Cu(I) catalyst, forming supramolecular
nanoreactors for the catalysis of CuAAC click reaction
in only water.
Normally, in the molecular structure of JDs, the
hydrophilic dendron is composed of poly(ethylene gly-
col),[18] amino,[19] hydroxyl[20] and carboxyl groups,[21]
while the hydrophobic part is often constructed of ali-
phatic chains with different length,[18] poly(benzyl
ether)[13] and so on. However, there are few reports on
the synthesis and functional applications of Janus
metallodendrimers.[16] Metallomacromolecules, also
named metal‐containing macromolecules and organome-
tallic macromolecules, include linear metallopolymers
and branched metallodendrimers, and are one of the
major classes of macromolecules discovered in the twenti-
eth century.[22–25] The unique combination of organic and
inorganic components in one macromolecular system
affords them a range of applications that span diverse
fields, such as emissive and photovoltaic materials,
nanopatterning, information storage, electrolysis, electro-
chemical devices, sensing, catalysis, artificial enzymes,
stimuli‐responsive materials, bioimaging and drug deliv-
ery.[26–31] Predictably, full benefit can be achieved by
incorporating various metal‐containing moieties into the
structure of JDs because of their unique electronic, cata-
lytic, magnetic and radioactive properties.
2 | EXPERIMENTAL
2.1 | General
Fc, methyl gallate and triethylene glycol monomethyl
ether were purchased from Energy Chemical, and used
directly. Azidomethylferrocene (6) was synthesized
according to previous reports.[46] All the other chemicals
used were of analytic grade, commercially purchased
and used as received. All the solvents used were dried
and freshly distilled.
In the work reported here, we designed a novel
Percec‐type ferrocene (Fc)‐containing dendron (7;
Scheme 1) as a mini JD. The hydrophobic part is com-
posed of only one Fc unit, while the hydrophilic one con-
tains three triethylene glycol (TEG) termini, and they are
connected by a 1,2,3‐triazole group through a copper(I)‐
catalyzed azide alkyne cycloaddition (CuAAC) click reac-
tion.[32] The combination of the amphiphilicity of JD 7
and the redox activity of the Fc moiety provides a multi-
functional material. Fc derivatives are typically stable for
both oxidized Fe(III) and reduced Fe(II) forms and
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were recorded at 25 °C with a Bruker AV II‐400 MHz
spectrometer. All the chemical shifts are reported in parts
per million (δ, ppm) with reference to tetramethylsilane
(TMS). Mass spectra were recorded using a GCMS‐
QP2010 Plus spectrometer. Infrared (IR) spectra were
recorded with an America Thermo Scientific Nicolet
iS10 FT‐IR spectrophotometer using KBr discs in the
range 400–4000 cm−1. UV–visible absorption spectra were
measured with a Shanghai Jinghua UV1900 UV–visible
spectrometer.
Dynamic
light
scattering
(DLS)
SCHEME 1 Synthetic route of amphiphilic triazolylferrocenyl Janus dendron 7

ZHAO ET AL.
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FIGURE 1 Schematic of JD 7 as nanoparticle stabilizer, drug carrier and supramolecular nanoreactor
measurements were conducted at 25 °C with a NanoZS
laser diffraction instrument (Malvern, UK). Scanning
electron microscopy (SEM) observations were conducted
with a JSM‐7500F field emission SEM instrument (JEOL).
Samples for SEM were prepared by casting a drop of the
solution on a silicon grid, followed by drying at room tem-
perature (r.t.).
found: 874.00 (M+), 896.44 (M + Na+). 1H NMR
(400 MHz, CDCl3, 25 °C, TMS, δ, ppm): 7.45 (s, 1H,
C═CH of triazole), 6.56 (s, 2H, benzene), 5.29 (s, 2H,
benzene‐CH2O), 4.61 (s, 2H, trazole‐CH2O), 4.45 (s, 2H,
Fc‐CH2), 4.28 (t, J = 3.6 Hz, 2H, sub. Cp, Cp = η5‐C5H5),
4.21 (t, J = 3.6 Hz, 2H, sub. Cp), 4.18 (s, 5H, free Cp),
4.13–4.10 (q, 6H, 3 × benzene‐OCH2), 3.84–3.53 (m,
30H, 3 × OCH2CH2OCH2CH2OCH2), 3.37 (s, 9H,
3 × OCH3). 13C NMR (100 MHz, CDCl3, 25 °C, TMS, δ,
ppm): 152.5, 137.7, 133.2, 107.2 (benzene), 144.7, 121.9
(C═C of triazole), 80.7 (free Cp), 69.0, 68.9, 68.8 (sub.
Cp), 72.1 (benzene‐OCH2), 72.3, 71.8, 70.6, 70.5, 70.4,
69.6 (CH2O), 68.6 (OCH2‐triazole), 63.4 (N‐CH2‐Fc),
58.9 (OCH3). Selected IR (KBr, cm−1): 2971 (νCH3), 1699
(νN═N), 1635, 1540, 1495, 1453 (νC═C,Ar), 1331 (νC─N),
1096 (νC─O─C), 1051 (νC─O─CH3), 802 (νFeII).
2.2 | Synthesis of Dendron 7
1,2,3‐Tris(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)‐5‐
((prop‐2‐yn‐1‐yloxy)methyl)benzene (5; 0.6 g, 0.95 mmol,
1.0 equiv.) and 6 (0.27 g, 1.14 mmol, 1.2 equiv.) were dis-
solved in 20 ml of tetrahydrofuran (THF). CuSO4⋅5H2O
(0.28 g, 1.14 mmol, 1.2 equiv.) aqueous solution (10 ml)
was added into the reaction mixture, followed by the
dropwise addition of a freshly prepared sodium ascorbate
(NaAsc; 0.45 g, 2.28 mmol, 2.4 equiv.) aqueous solution
(10 ml) to obtain THF–water in a ratio of 1:1. The
obtained mixture was stirred for 72 h at r.t. under nitro-
gen, and then vacuumed to remove THF. The residue
was dissolved in dichloromethane (10 ml) and aqueous
ammonia (10 ml), and stirred for 30 min to remove the
copper ions trapped inside the target compound as
[Cu(NH3)2(H2O)2]2+. The organic layer was collected,
dried by anhydrous Na2SO4 and evaporated under
reduced pressure. Purification was conducted by column
chromatography with CH2Cl2–methanol (1% → 50%) as
eluent to afford 7 as orange‐yellow oil. Yield: 0.58 g,
70%. MS (ESI m/z), calcd for C42H63FeN3O13: 873.82;
2.3 | Synthesis of AgNPs‐1 using NaBH4 as
reductant
Dendron 7 (62.5 mg, 7.44 × 10−2 mmol, 2 equiv.) and
NaBH4 (2.8 mg, 7.44 × 10−2 mmol, 2 equiv.) were
dissolved in distilled water (25 ml) in a Schlenk flask,
and AgNO3 (6.3 mg, 3.72 × 10−2 mmol, 1 equiv.) aqueous
solution (30 ml) was then injected dropwise into the flask
under nitrogen atmosphere with vigorous stirring. The
obtained solution was further stirred for 1 h at 30 °C
under nitrogen, and the color changed from orange‐
yellow to brownish red. Dialysis was conducted against

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ZHAO ET AL.
a large volume of distilled water before the produced
AgNPs‐1 was analyzed.
W1
W2
DLC ð%Þ ¼
×100
2.4 | Synthesis of AgNPs‐2 using 7 as
reductant
W1
EE ð%Þ ¼
×100
W3
AgNO3 (6.3 mg, 3.72 × 10−2 mmol, 1 equiv.) was dissolved
in distilled water (30 ml), and injected dropwise into a vig-
orously stirred aqueous solution (25 ml) of 7 (62.5 mg,
7.44 × 10−2 mmol, 2 equiv.) in a Schlenk flask. The
obtained mixture was stirred for 1 h at 30 °C under nitro-
gen. The color changed immediately from orange‐yellow
to green. The obtained AgNPs‐2 was purified by dialysis
against a large volume of water before analysis.
where W1 is the RhB encapsulated (mg) by vesicles of 7,
W2 is the amount of 7 (mg) used, while W3 is the RhB
added during encapsulation process. The standard curve
of RhB (Figure S32) obtained in distilled water was used
to determine the value of W1.
2.8 | In Vitro drug release
An amount of 1 ml of the RhB‐loaded micelles, obtained
as described above, was added into a dialysis tube
(MWCO: 3500 g mol−1), and immersed at r.t. in 25 ml of
FeCl3 solution (3 mg ml−1) in which FeCl3 was used as
the oxidant to trigger the redox release of encapsulated
RhB. At different intervals, a 2 ml dialysate sample was
taken out and 2 ml of fresh FeCl3 solution was supple-
mented. The absorbance of the obtained sample was
determined using a UV–visible spectrometer at 552 nm,
and the amount of RhB released was calculated using
the standard curve of RhB.
2.5 | Synthesis of AuNPs‐1 using NaBH4 as
reductant
Compound 7 (52.4 mg, 6.00 × 10−2 mmol, 5 equiv.) and
NaBH4 (1.6 mg, 6.00 × 10−2 mmol, 5 equiv.) were
dissolved in distilled water (10 ml) in a Schlenk flask,
and HAuCl4 (4.1 mg, 0.01 mmol, 1 equiv.) dissolved in
water (15 ml) was then injected dropwise into the Schlenk
flask and further stirred for 1 h at 30 °C under nitrogen.
The color changed immediately from orange‐yellow to
black‐purple. The reaction mixture was purified by dialy-
sis against a large volume of water before analysis.
2.9 | Synthesis of water‐soluble catalyst 7‐
CuI
2.6 | Synthesis of AuNPs‐2 using 7 as
reductant
CuSO4⋅5H2O (7.8 mg, 4.75 × 10−2 mmol, 1 equiv.) dis-
solved in 1 ml of degassed water was added into 2 ml of
an aqueous solution of 7 (41.6 mg, 4.75 × 10−2 mmol, 1
equiv.) in a dry round‐bottom flask. The obtained mixture
was stirred at r.t. for 30 min under nitrogen. Then, NaAsc
(47 mg, 2.37 × 10−2 mmol, 5 equiv.) in 2 ml of degassed
water was added dropwise to the solution, and further
stirred at r.t. for 2 h to yield the 7‐CuI catalyst.
HAuCl4 (3.4 mg, 0.01 mmol, 1 equiv.) dissolved in water
(12.5 ml) was injected dropwise into a vigorously stirred
aqueous solution (25 ml) of 7 (52.4 mg, 0.06 mmol, 6
equiv.) in a Schlenk flask, and further stirred for 1 h at
30 °C under nitrogen. The color changed immediately
from orange‐yellow to black‐purple. The obtained
AuNPs‐2 was purified by dialysis against a large volume
of water before analysis.
2.10 | Click reaction catalyzed by 7‐CuI
Phenylacetylene (12; 47 mg, 2.5 × 10−2 mmol), 1‐azido‐
2‐(2‐(2‐methoxyethoxy)ethoxy)ethane (11; 27 mg,
2.61 × 10−2 mmol) and the desired 7‐CuI catalyst
(0.125 mmol of CuI) were added successively into a
round‐bottom flask containing 6 ml of degassed water
under nitrogen. The obtained mixture was stirred for 24 h
at 30 °C under nitrogen. The final product was extracted
from water with CH2Cl2, and the obtained organic layer
was dried with anhydrous Na2SO4, and the solvent was
removed in vacuo. The targeted triazole product 13 was
purified by silica chromatography with CH2Cl2–methanol
as eluent.
2.7 | Drug loading by self‐assembled 7
Dendron 7 (15 mg, 0.017 mmol) was dissolved in 7.5 ml of
THF, and then 1 ml of a THF solution of RhB (1 mg ml−1
)
was added, and stirred for 2 h, followed by slowly adding
deionized water (7.5 ml) via a syringe pump. After the
addition, the resulting solution was further stirred at r.t.
for 4 h. Dialysis (molecular weight cutoff (MWCO):
3500 g mol−1) was conducted against deionized water
for 48 h to remove the unloaded RhB. The drug loading
content (DLC) and the encapsulation efficiency (EE) were
calculated according to the following formulas:

ZHAO ET AL.
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click reaction, while the Cp carbons of Fc moiety are
located at 80.7, 69.0, 68.9 and 68.8 ppm. All the other
peaks of the 13C NMR spectrum were clearly assigned
and matched well with the structure of 7. The mass spec-
trum of 7 (Figure S25) shows the molecular peak at
874.00 Da, in good agreement with the theoretical value
of 873.82 Da. The UV–visible spectrum of 7 (Figure S26)
shows a maximum absorption (λmax) at 428 nm corre-
sponding to the d–d* transition of Fc group. The IR
spectrum (Figure S27) also provides complementary
information for the structure of 7.
The target product 7 was obtained as orange‐yellow
oil, and shows good solubility in water and common
organic solvents such as CH2Cl2, chloroform, THF, ace-
tone, acetonitrile, methanol, dimethylformamide (DMF)
and dimethylsulfoxide (DMSO). This amphiphilic prop-
erty opens a door for dendron 7 to be applied in the
fields of nanometric materials, drug delivery and cataly-
sis (vide infra).
3 | RESULTS AND DISCUSSION
3.1 | Click synthesis and structure of
Dendron 7
The new amphiphilic JD 7 was prepared through the
CuAAC click reaction between 6 and propargyl‐function-
alized dendron 5 containing three TEG termini that was
prepared following the route shown in Scheme 1. The
starting methyl gallate (1) reacted with 2‐(2‐(2‐
methoxyethoxy)ethoxy)ethyl tosylate (2) yielding the cor-
responding tris‐TEG dendron 3 bearing methyl ester
group that was then reduced to hydroxymethyl group by
LiAlH4 to afford the benzyl alcohol derivative 4. The reac-
tion of 4 with propargyl bromide in the presence of potas-
sium tert‐butoxide resulted in the key intermediate alkyne
dendron 5. The click reaction of 5 and 6 was catalyzed in
THF–water (1:1) by the catalytically active CuI species
generated from CuSO4 and NaAsc in excess.
Figure 2 shows the 1H NMR spectrum of 7. The
appearance of the signal for the triazolyl proton at
7.45 ppm, the characteristic signal of five free Cp protons
at 4.18 ppm, and that of the substituted Cp protons at 4.28
and 4.21 ppm demonstrate the success of the click
reaction and the integrity of the Fc group. The single peak
at 6.56 ppm originates from the protons of benzene ring,
while the peak for methylene protons connecting to ben-
zene ring is observed at 5.29 ppm, and the signals of meth-
ylene protons close to triazole unit were found at 4.61 and
4.45 ppm, respectively. The signals of the CH2 protons of
the three TEG termini are concentrated at 4.10–4.13 and
3.53–3.84 ppm, respectively, while the singlet peak at
3.37 ppm corresponds to the nine oxymethyl protons
(─OCH3). In the 13C NMR spectrum of 7 (Figure S24),
the peaks at 144.7 and 121.9 ppm correspond to the car-
bons of triazoly unit, further confirming the successful
3.2 | AgNPs‐1 and AuNPs‐1 stabilized by
Dendron 7
The TEG tails of dendron 7 bring excellent solubility in
aqueous media and biocompatibility, and the ‘click’
chemistry further offers a simple 1,2,3‐triazole ligand used
to stabilize silver and gold NPs that occupy a central place
in nanoscience and nanotechnology owing to their vari-
ous applications in catalysis, materials science, optical
biosensing, and nanomedical diagnostics and therapeu-
tics.[47,48] Thus, the JD 7 was firstly applied as a stabilizer
to fabricate AgNPs and AuNPs in water system using
NaBH4 as a reductant.
A one‐step process was adopted to prepare AgNPs‐1
and AuNPs‐1 stabilized by Fc–triazole‐containing
dendron 7 in aqueous solution. AgINO3 and HAuIIICl4
FIGURE 2 1H NMR spectrum (400 MHz) of 7 in CDCl3

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ZHAO ET AL.
FIGURE 4 UV–visible spectra of AuNPs‐1 (a) and AuNPs‐2 (b)
FIGURE 5 DLS curves of AgNPs and AuNPs
were reduced to Ag0 and Au0, respectively, by dropwise
addition of their aqueous solution into an aqueous solu-
tion of 7 in the presence of NaBH4 at 30 °C under nitrogen
atmosphere with vigorous stirring. The stoichiometry of
AgI:ligand:NaBH4 was 2:2:1, while that of AuIII:ligand:
NaBH4 was 5:5:1. Obvious color changes were observed
from orange‐yellow to brownish red for AgNPs‐1
(Figure 3a) and black‐purple for AuNPs‐1 (Figure 4a).
The excess ligand and salts were removed from the NP
solution by dialysis against a large amount of deionized
water. The obtained NPs were characterized using UV–
visible spectroscopy, SEM, energy‐dispersive X‐ray spec-
troscopy (EDS) and DLS.
For AgNPs‐1, the UV–visible spectrum (Figure 3a)
shows λmax at 422 nm corresponding to the characteristic
surface plasmon band (SPB) of Ag0 and d–d* transition of
Fc unit. Considering that NaBH4 is a much stronger and
faster‐acting reducing reagent than Fc,[36] no oxidation
of Fc took place during the preparation of AgNPs‐1.
The average core size determined using SEM (Figure
S28) is 74 nm, and the shape of the AgNPs‐1 core is
quasi‐spherical. DLS (Figure 5) provides a hydrodynamic
radius of 109 nm with a polydispersity index (PDI) of
0.215 for AgNPs‐1. Diameters determined using DLS are
typically larger than those determined using SEM. The
size difference between SEM and DLS may arise from
their different determination conditions. The size distri-
bution of AgNPs‐1 determined using DLS reflects the
dimensions of both the swollen core and the stretched
shell, but the size determined using SEM reflects only
conformations in the dry state. EDS of AgNPs‐1 (Figure
S28) confirms the presence of Ag and the elements (i.e.
C and O) contained in dendron 7.
For AuNPs‐1, the SPB of Au0 is observed at 527 nm as
seen in the UV–visible spectrum (Figure 4a), and the SEM
image (Figure S29) revealed the average core size of these
AuNPs as being 26 nm, which is also smaller than the
value of 87 nm (PDI = 0.223) determined using DLS
(Figure 5). The EDS result (Figure S29) provides indisput-
able evidence for the presence of Au.
FIGURE 3 UV–visible spectra of AgNPs‐1 (a) and AgNPs‐2 (b)

ZHAO ET AL.
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green for AgNPs‐2 (Figure 3b) and black‐purple for
AuNPs‐2 (Figure 4b).
3.3 | AgNPs‐2 and AuNPs‐2 prepared using
Dendron 7 as reductant
In these reactions, AgI and AuIII were reduced to cor-
responding Ag0 and Au0 atoms that form AgNPs‐2 and
AuNPs‐2, respectively, while the Fc unit was oxidized to
ferricenium salts (nitrate and chloride, respectively).
Thus, the Fc moiety works not only as the capping agent
in its oxidized form but also as the reductant. The
obtained NPs are stabilized by the ferricenium triazole
ligand, with stabilization resulting from the positive syn-
ergy between the electrostatic factor and the triazolyl
ligand coordination to the NP surface (Figure 1). As
shown in Figure 3(b), the oxidation of Fc to ferricenium
was successfully recorded using UV–visible spectroscopy,
with the band at 632 nm corresponding to the ferricenium
unit, while the peak at 440 nm is assigned to the SPB of
Ag0. For AuNPs‐2, the UV–visible spectrum (Figure 4b)
shows a strong λmax at 554 nm originating from the SPB
of Au0 that covers the ferricenium band.
The SEM image in Figure 6 reveals the rod‐like mor-
phology of AgNPs‐2 with a width of about 100 nm and
length of 710 nm or so. DLS (Figure 5) analysis provides
an average size of 180.9 nm with a PDI of 0.203. EDS
(Figure 6) results further confirm the coexistence of Ag
and Fe elements, illustrating that dendron 7 is not only
a reductant but also a protective agent. Furthermore,
AgNPs‐2 is much larger than obtained from NaBH4
reduction (AgNPs‐1), because the later reductant is much
stronger than Fc, and the NP size is linked to the reduc-
tion rate that depends on the driving force.
The successful fabrication of AgNPs‐1 and AuNPs‐1 con-
firmed the stabilization of dendron 7 for nanometals, and
inspired us to explore further the possibility of preparing
AgNPs‐2 and AuNPs‐2 for comparison, in which
dendron 7 was applied as reductant due to its redox‐
sensitive Fc unit. Notably, Fc has an oxidation potential
of 0.4–0.5 V versus SCE depending on the solvent, and
thus Fc and Fc‐containing derivatives are useful reducing
agents towards strong oxidants owing to the relative sta-
bility, a least for a short time, of the ferricenium salts.[49]
Polymers and dendrimers containing Fc, biferrocene and
pentamethylferrocene have been used to reduce Ag(I)
and Au(III) that were coordinated to nitrogen ligands
such as triazoles, leading to the formation of noble metal
NPs.[33–40] However, to the best of our knowledge, there
are only few reports of the preparation of AgNPs and
AuNPs using water‐soluble Fc‐containing macromole-
cules as reductants in water system, let alone Janus
ferrocenyl dendrimers or dedrons, although there is a
recent report on the formation of AuNPs induced and
stabilized by water‐soluble triazine dendrons with a dia-
zonium salt,[50] in which the reductant for AuIII was
NaBH4, not the synthesized dendrons.
Here, the simple triazolylferrocenyl JD 7 was oxidized
with AgINO3 and HAuIIICl4 to form AgNPs‐2 and
AuNPs‐2 in interaction with triazolylferricenium salts.
During the preparation of AgNPs‐2 and AuNP‐2, no
external reductant was involved. AgINO3 and HAuIIICl4
are reduced to Ag0 and Au0, respectively, by dropwise
injection of their aqueous solution into an aqueous solu-
tion of dendron 7 at 30 °C under nitrogen atmosphere
with vigorous stirring. A stoichiometry of 1:2 was adopted
for AgI:7, while that of AuIII:7 was 1:6. The original
orange‐yellow of systems was changed immediately to
The core size of AuNPs‐2 determined using SEM
(Figure 7) is 20 nm, while DLS (Figure 5) provides a size
of 94 nm with a PDI of 0.196. The major size difference
between SEM and DLS perhaps was caused by the slight
aggregation in the NP system. These results indicated
AuNPs‐2 was slightly larger than AuNPs‐1. The size dif-
ference between them may be result from the difference
FIGURE 6 SEM image (left) and EDS (right) of AgNPs‐2

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ZHAO ET AL.
FIGURE 7 SEM image (left), EDS (middle) and size distribution (right) of AuNPs‐2
of the reduction and stabilization rates in each case.
Indeed, the stabilization in AuNPs‐2 is stronger com-
pared to AuNPs‐1 because of the additional electrostatic
stabilization of the former. EDS also demonstrates the
coexistence of Au and Fe elements in this system.
Thus, using the new Janus Fc‐containing dendron 7 as
an amphiphilic stabilizer or reductant, both stable AgNPs
and AuNPs could be successfully fabricated in water sys-
tem, and their morphology and size are different accord-
ing to the corresponding conditions.
FIGURE 8 SEM images and size distributions of micelles self‐assembled from dendron 7 (top) and RhB‐loaded micelles (bottom)

ZHAO ET AL.
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The fluorochrome RhB was then used as a model drug
to be encapsulated by dendron 7 micelles using the injec-
tion method. The slow injection of a THF solution of
dendron 7 and RhB into deionized water, followed by
4 h of vortex mixing, resulted in micelles loaded with RhB
(Figure 8, bottom). These micelles also show a spherical
shape with an average size of 32 nm as determined using
SEM. The unloaded RhB and THF solvent were removed
by dialysis against deionized water. The successful load-
ing of RhB into the formed micelles was confirmed by
comparing the UV–visible absorption spectra of the dialy-
sate (RhB‐unloaded micellar solution) and the RhB‐
loaded micellar solution. The latter exhibits a characteris-
tic absorption peak of RhB at 552 nm (Figure S31). The
encapsulated content of RhB was then determined using
the standard curve of RhB (Figure S32) drawn by its λmax
at 552 nm. Both the drug loading content and the encap-
sulation efficiency for the obtained spherical micelles
were calculated to be 1.52%.
To investigate the controlled release property of the
encapsulated RhB, FeCl3, as an oxidant to Fc complex,
was added into the micelle system. The oxidation of the
Fc moiety to cationic FeIII species is associated with an
increase of the polarity and charge. This feature has been
employed to modulate the self‐assembly or disassembly of
Fc‐containing polymers.[51–54] Here, the stimuli‐induced
release of the payload was determined by monitoring the
decrease of RhB UV–visible absorption intensity with
time in the aqueous release medium after application of
stimuli. As shown in Figure 9 (left), the cumulative
release of RhB reaches almost 50% after 27 h in the solu-
tion of FeCl3 (3 mg ml−1), and thereafter no great increase
in release is observed even when the time is prolonged to
60 h. The possible triggering mechanism is based on
increased coulombic repulsion interaction[51–54] between
the positively charged ferrocenium produced from the
3.4 | Drug loading and redox‐responsive
release for micelles self‐assembled from
Dendron 7
Amphiphilic Janus dendrimers and dendrons feature
various well‐defined and complex self‐assembled struc-
tures such as micelles, vesicles, cubosomes, discs, tubu-
lar vesicles, helical ribbons and bilayered vesicles
called dendrimersomes, and their potential applications
for drug delivery.[6–18] Redox‐responsive Fc‐containing
macromolecules have recently gained considerable
attention due to their potential in controllable delivery
and release in physiological environments, where redox
reactions are widely and constantly present.[26] The
reversible conversion between hydrophobic Fc group
and hydrophilic ferrocenium by chemical and electro-
chemical reduction is a great advantage for the con-
struction of reversible self‐assembly and disassembly
systems, and thus afford Fc‐containing macromolecules
as the optimal candidates for redox‐stimuli‐responsive
drug carriers.[51–54] Here, dendron 7 possesses not only
the asymmetric and amphiphilic characters of Janus
structures, but also the redox‐sensitive Fc moiety; thus
it was speculated that it would self‐assemble into
micelles used to load drugs for oxidation‐triggered
release as shown in Figure 1.
As expected, spherical micelles (Figure 8, top) were
formed by the self‐assembly of 7 in aqueous solution.
The size of the freshly prepared micelles ranges from 14
to 35 nm as determined using SEM, and the mean size
is 27 nm. Notably, in a typical micelle, the central part
exhibits dark color, while a light color is observed at the
periphery. The dark center is attributed to the inward
aggregation of the dense Fc‐containing hydrophobic head,
and the light periphery is owing to the organic hydro-
philic TEG tails.
FIGURE 9 Oxidation‐responsive release profile of RhB from micelles using FeCl3 as an oxidant (left), and the corresponding time‐
dependent DLS curves (right)

10 of 12
ZHAO ET AL.
oxidation of Fc by FeCl3, which destabilizes the structural
stability of micelles and results in the release of interior
RhB. This point was further confirmed from the corre-
sponding time‐dependent DLS curves (Figure 9, right).
Before the addition of FeCl3, the DLS curve of RhB‐loaded
micelles showed a single size distribution of 42.6 nm with
a small PDI value of 0.06. Obviously, oxidation of Fc units
by FeCl3 led to increased average sizes with wide size dis-
tribution ranges. Along with the prolonged reaction time,
the size of micelles gradually increased due to the
increased repulsive interaction between the formed posi-
tively charged FeIII species; thus the encapsulated RhB
could release easily through the increased gap in micelles.
Typically, the size reached a maximum of 94.2 nm at 32 h.
At the same time, small micelles with a size of 8–15 nm
also appeared subsequently because the hydrophilic
ferrocenium increased the solubility of oxidized 7 in
water, resulting the sharply reduction of aggregated mol-
ecules in some self‐assemblies. This disassembly process
further promoted the release of RhB. Following the
increase of disassembled dendron molecules, the average
size of micelles gradually decreased. For example, at
60 h, reduced micelles with a size of 53.6 nm were
observed. Further, the increased PDI values also demon-
strated the disassembly of drug‐loaded micelles.
FIGURE 10 Comparison of 1H NMR signals of triazole proton of
7 alone, with CuII and CuI
precatalyst 7‐CuII, then CuII is reduced in situ to CuI for
CuAAC click catalysis. The coordination of CuII and CuI
1
to the triazole ring of 7 has been demonstrated using H
NMR spectroscopy (Figure 10). The addition of equimolar
CuSO4⋅5H2O to an aqueous solution of 7 leads to a shape
change of the NMR signal of the triazole proton of 7 at
7.448 ppm from original sharp peak to a broad one owing
to the paramagnetic CuII species. When NaAsc is added to
reduce CuII to CuI, the NMR signal of the triazole proton
shifts from 7.447 to 7.451 ppm, indicating the complexing
of the triazole ring to CuI.
The catalytic efficiency of the CuAAC catalyst 7‐CuI
involved in this system was tested for the reaction
between 11 and 12 (Scheme S3) with various amounts of
catalyst (0.2, 0.5, 1.0 and 2.0 equiv. per 11, respectively)
in only water with stirring for 24 h at 30 °C. The obtained
triazole product 13 was confirmed from its 1H NMR spec-
trum (Figure S34), which shows the characteristic
triazolyl proton at 7.99 ppm. Using the water‐soluble cat-
alyst 7‐CuI, the CuAAC click reaction can be carried out
in only water, and as summarized in Table 1, the yield
improves with an increase of catalyst 7‐CuI used. When
the amount of catalyst is 1.0 equiv., the isolated yield
reaches 94.1% (nearly quantitative), comparable to 98.6%
(entry 5) when the reaction is conducted in THF–water
(1:1) using the classic and original catalyst
CuSO4⋅5H2O + NaAsc.
In conclusion, the prepared dendron 7 can self‐assem-
ble into nanoscale micelles as a potential candidate for
drug loading and the subsequent redox‐responsive release
in drug delivery.
3.5 | Catalysis of CuAAC click reaction in
water
Various triazole ligands have already been shown to play a
role in stabilization of metal ions and their nanoparticles
to facilitate corresponding catalysis processes.[45,55–58]
Considering the excellent self‐assembly property of
dendron 7 in water, and the excellent metal‐complexing
ability of the riazole group, we further explored the possi-
bility of using the micelles self‐assembled by dendron 7 as
supramolecular nanoreactors to catalyze reactions in only
water.
TABLE 1 CuAAC reaction using various amounts of CuI catalyst
with respect to azide 11
CuAAC is the most common click reaction allowing
the linking together of two organic, bioorganic or other
functional molecular fragments, and has extensive appli-
cations in the areas of inorganic, organic, biomaterial
and polymer chemistry. Here, the CuAAC in only water
was investigated using dendron 7 micelles as molecular
nanoreactors. As shown in Figure 1, a new water‐soluble
catalyst, 7‐CuI, was prepared by amphiphilic dendron 7
in the presence of CuSO4⋅5H2O and NaAsc with stirring
in only water. After adding CuSO4⋅5H2O to an aqueous
solution of 7, CuII coordinates the triazolyl ligand as
Entry
1a
CuI (equiv.)
Yield (%)
0.2
61.2
2a
3a
4a
5b
0.5
1.0
2.0
2.0
87.3
94.1
96.0
98.6
aReaction conducted using 7‐CuI in only water.
bReaction carried out in THF–H2O (1:1) using classic catalyst
CuSO4⋅5H2O + NaAsc.

ZHAO ET AL.
11 of 12
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4 | CONCLUSIONS
In summary, we report the preparation and multifunc-
[9] D. R. Sikwal, R. S. Kalhapure, T. Govender, Eur. J. Pharm. Sci.
2017, 97, 113.
[10] A. Walther, A. H. Müller, Chem. Rev. 2013, 113, 5194.
tional
applications
of
a
novel
amphiphilic
triazolylferrocenyl JD (7) with three TEG termini. JD 7,
easily synthesized by CuAAC click reaction between
azidomethylferrocene and corresponding TEG‐termi-
nated acetylene, provides a convenient neutral ligand for
the stabilization of AgNPs‐1 and AuNPs‐1 in water with
NaBH4 as the reductant, and a cationic ferricenium stabi-
lizer for AgNPs‐2 and AuNPs‐2 in the system without
NaBH4, in which the Fc moiety was used as mild stoichio-
metric reducing agent. In both cases, the role of the 1,2,3‐
triazole group was the stabilization of the NPs. The
amphiphilic property of JD 7 led to the formation of
micelles by self‐assembly, and the encapsulated model
drug RhB can be released by the oxidation of the
contained Fc unit with FeCl3 as an oxidant, which proves
the feasibility to use JD 7 as a smart drug carrier. More-
over, a new supramolecular nanoreactor was successfully
constructed by utilizing the good self‐assembly character-
istic of 7 and the precise complexing ability to copper ions
of its triazole group, and which was confirmed to be effi-
cient for the catalysis of CuAAC click reaction in only
water. As a class of novel Janus metallodendrimers, this
Fc‐containing minidendron could open up new avenues
for diverse applications, especially in the areas of function
materials and nanomedicines.
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How to cite this article: Zhao L, Ling Q, Liu X,
et al. Multifunctional triazolylferrocenyl Janus
dendron: Nanoparticle stabilizer, smart drug carrier
and supramolecular nanoreactor. Appl
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